The present invention relates to a compressor for use in refrigeration systems such as air-conditioners and heat pumps, and in particular to a variable capacity compressor which has dual motor-crankshaft-pump units mounted within a common housing and having a common inlet and outlet.
In certain refrigeration systems, such as air-conditioners and heat pumps for commercial and residential dwellings, it is desirable to vary the capacity of the refrigerant compressor in order to more closely match the heating or cooling requirements. Although it is possible to utilize a compressor which is large enough to handle even the highest demand, such a compressor runs less efficiently during periods of low demand, thereby increasing energy costs.
One technique for providing variable capacity in a compressor, is to drive the compressor by means of a two speed motor. Such a motor involves relatively costly switching apparatus, and often runs at lower efficiency than a single speed motor.
U.S. Pat. No. 2,012,704 discloses a motor-compressor unit for refrigeration apparatus wherein a plurality of motor-compressors are housed within a single shell, and wherein the units are coaxially mounted. The motor-compressor units have separate crankcases which are physically separated thereby unduly increasing the size of the unit. Furthermore, due to the fact that the crankshafts are horizontal and in line, lubrication of the system is much more complicated. It is the purpose of this system to combine a plurality of identical and complete motor-compressor units into one complete unit of greater capacity than either of the units by itself, rather than to provide a compressor of variable capacity as in the present invention.